A fluoroolefin copolymer is suitably used as a coating resin. The coating resin is required to have good storage stability in its solution state. Further, such a resin solution is preferably colorless.
Patent Document 1 relates to a method for producing a fluorinated copolymer, and discloses that a monomer mixture comprising a fluoroolefin and an alkyl vinyl ether is copolymerized in a polymerization medium containing a lower alkyl benzene and a component having a boiling point lower than the lower alkyl benzene in the presence of an alkali metal carbonate, whereby the copolymerization reaction can be smoothly proceeded, and storage stability of a varnish containing the formed copolymer can be obtained. As an example of the alkali metal carbonate, potassium carbonate is mentioned.
On the other hand, it is known to use hydrotalcite at the time of producing a fluoroolefin copolymer in order to suppress gelation during the polymerization or to prevent corrosion of a base material by an acid component in the polymer solution (Patent Documents 2 to 4).
Patent Document 2 relates to a method for producing a fluoroolefin copolymer having hydroxy groups and discloses a method wherein a monomer mixture comprising a fluoroolefin and a vinyl ether having a hydroxy group is radical-polymerized in the presence of at least one member selected from a metal oxide, a metal hydroxide and an additive A made of an anion exchange resin. As a preferred example of the metal hydroxide, hydrotalcite is mentioned. It is disclosed that by using the additive A, it is possible to obtain effects to prevent gelation during the polymerization and to prevent an increase in the molecular weight distribution of the formed copolymer.
Patent Document 3 discloses a method wherein a fluoroolefin and another monomer are radical-polymerized in a solution to prepare a polymer solution, and then, the polymer solution is contacted with a basic solid material for neutralization treatment to neutralize an acid component contained in the polymer solution thereby to prevent formation of corrosion inside of a tin can. As an example of the basic solid material, hydrotalcite is mentioned.
In Patent Document 4, it is disclosed that a fluorinated vinyl monomer and another monomer are polymerized in the presence of a basic solid material having an average particle diameter of at most 1 μm to produce a resin composition containing a fluorinated vinyl copolymer and the basic solid material, whereby corrosion can be prevented even in a case where a coating film formed by using such a resin composition, is formed on a metal plate. As an example of the basic solid material, hydrotalcite is mentioned.